Spectroscopic orbits and variations of RS Oph
The aims of our study are to improve the orbital elements of the giant and to derive the spectroscopic orbit for the white dwarf companion. Spectral variations related to the 2006 outburst are also studied. The spectroscopic orbits have been obtained by measuring the radial velocities of the cool component absorption lines and the broad Halpha emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. A new period of 453.6 days and a mass ratio, q=M_g/M_h=0.59 were determined. Assuming a massive white dwarf as the hot component, M_h= 1.2-1.4 M_{\odot}, the red giant mass is M_g= 0.68-0.80 M_{\odot} and the orbit inclination, i = 49-52^{\circ}. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the LiI doublet in RS Oph and its radial velocities fit very well the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 km/s and two other extended emission components at -200 and +150 km/s. These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane.